The present invention relates to a control system for plastics processing machines and handling devices for such machines, and more particularly to a controller for plastics processing machines with a serial bus system and real-time processing requirements.
Control systems with digital peripheral equipment for plastics processing machines use bus systems, in particular serial bus systems, meeting real-time requirements for communicating between sensors and/or actuators and the central processor (CPU), hereinafter also referred to as central processing unit. Intensive competition has rapidly lowered the cost-efficiency ratio of CPU units. Conversely, the capabilities of real-time-capable, serial bus systems have progressed at a much slower pace. In addition, in particular when digital sensors or actuators are used, complex protocols have to be processed for calibration, identification of the manufacturer or adaptation of drivers from different manufacturers. The increased complexity of these programs require a greater bandwidth of the bus systems and more CPU resources, wherein system functions in a separate CPU/RAM configuration are economically difficult to implement in small quantities.
German patent publication DE 199 58 790 C2 describes a machine for producing parts made of plastic or rubber, whereby a control device is subdivided into at least a first and a second functional unit. The first functional unit measures an actual temperature value, whereas the second functional unit performs control functions and outputs the control signals. DE 199 58 790 C2 addresses the problem of providing a decentralized input/output system that does not require additional installation space and manufacturing expenses. In addition, the wiring complexity should be minimized to save cost. This problem is solved by implementing in particular a portion of the functional unit with a control device in a plug connector which is connected via a field bus, e.g. a CAN-bus, with the actual central controller. The electronics contained in the plug connector can include, for example, an ASIC (application-specific integrated circuit), a microprocessor and a power supply. The ASIC converts the analog measurement values to digital signals. The microprocessor controlled the ASIC and performs the computation, linearization, cold-junction-compensation and transmission to the field bus controller.
In addition to using thermocouples as sensors, DE 199 58 790 C2 describes the possibility of providing in a controller additional digital outputs which can be connected with other sensors, for example core pullers, limits switches or proximity switches.
The sensors or actuators (e.g., heating tapes) mentioned in DE 199 58 790 C2 all represent components which operate relatively slowly and typically do not require a high resolution.
The problem addressed by the present invention, on the other hand, relates to the large burden placed on the central processors by the bus communication, in particular with rapidly changing variables (e.g., rapidly changing mechanical variables) with a high resolution. When using such sensors and actuators, it may happen that significant resources of the CPU are used (up to 40%) by the bus communication, including other tasks like signal pre-processing, driver adaptation, calibration, etc. These resources are then not available to the central processor or processing unit for actual computational and control tasks.
European Pat. No. EP 0 917 034 describes a method for remote monitoring and/or remote maintenance of an injection molding machine. The injection molding machine is provided with an SPS with at least one CPU for controlling the actuators of the injection molding machine in real-time. Data are transmitted between the injection molding machine and a remote monitoring station located at a distal location for remote monitoring and/or remote maintenance. As described in EP 0 917 034, several actuators and sensors are connected via inputs and outputs to a real-time controller. The inputs and outputs can include a digital card or an analog card. However, EP 0 917 034 does not disclose that these cards are provided with pre-processing units. Accordingly, the inputs and outputs represent conventional interfaces which for high data transmission rates require an increased communication bandwidth over a real-time-capable bus systems.
U.S. Pat. No. 5,901,058 describes a system and a method for achieving heterogeneous data flow in control systems. A server is connected with a plurality of controllers via a bus system, with the controllers operatively connected via a bus system with individual input/outputs stations which provide communication with sensors and actuators. However, this reference does not suggest a direct connection of a plurality of actuators to an input/output as well as the use of ASICs or FPGAs (field-programmable gate arrays) in the input/output devices for decreasing the bandwidth requirements.
It would therefore be desirable and advantageous to provide an improved device for reducing the communication bandwidth requirements of real-time-capable bus systems, in particular serial bus systems, of plastics processing machines and associated handling devices, which obviates prior art shortcomings and is able to specifically free up computing capacity in the CPU.